FIG. 1 illustrates a conventional resistive touch panel. The panel includes a front sheet 101 and a back sheet 102. To both front and back sheets 101-102 are applied a continuous resistive coating. The front sheet 101 is typically composed of a clear flexible material, while the back sheet 102 is typically a clear rigid piece material. The front and back sheets 101-102 are separated by insulating spacer dots (not shown). Pressure applied to the front sheet 101 causes its continuous resistive coating to contact the continuous resistive layer on the back sheet 102. The point of contact closes a circuit. The voltage drop across the back sheet 102 between the Y edge and the L edge of the back sheet is used to measure the position of the contact in the Y direction. The voltage drop across the front sheet 101 between the X edge and the H edge of the front sheet 101 is used to measure the position of the contact in the X direction.
FIG. 2 illustrates a controller circuit for the conventional resistive touch panel. The controller circuit 200 includes four analog-to-digital converters (A2D) 201 and a microcontroller 202. The controller circuit 200 drives a current through one of the resistive coatings by connecting one edge to the drive voltage and the other edge to ground. The controller circuit 200 switches between driving the current through the resistive coating on the front sheet 101 and the resistive coating on the back sheet 102. The voltage level of the points of contact between the front and back coatings is continuously converted by the A2D's 201 and monitored by the microcontroller 202 for voltage drops by measuring the voltage on the un-driven coating.
However, the microcontroller 202 assumes that any touch of the panel is a single touch with a small point contact. Thus, when the touch has a large contact area, such as when a user places a palm onto the panel, or when the touch is a multiple point touch, the value measured s from the large contact area or the multiple points is an average, resulting in a single touch coordinate result.
Accordingly, there exists a need for an improved resistive touch panel. The improved resistive touch panel should be able to determine between small and large areas of contact and multiple point contacts by detecting adjacent contact areas. The present invention addresses such a need.